Bone anchors may be used in orthopedic surgery to fix bone during the healing or fusion process. In spinal surgery, bone anchors may be used with spinal fixation elements, such as spinal rods, to stabilize multiple vertebrae either rigidly, in which no relative motion between the vertebrae is desired, and dynamically, in which limited, controlled motion between the vertebrae is desired. In certain procedures, such as minimally invasive procedures, it may be desirable to deliver the bone anchor to the vertebra over a guide wire or other guidance instrument. To facilitate this, bone anchors may be cannulated, i.e., may have a central passage through the bone anchor that is sized to receive the guide wire. One problem with the use of cannulated bone anchors is that when such bone anchors are used in a procedure without a guide wire, for example, in an open or non-minimally invasive procedure, it may be difficult to start the bone anchor in the proximal surface of the bone unless either an opening in the bone is pre-threaded using a tap or other instrument or the surgeon applies a significant distal force on the bone anchor. Accordingly, there is need for improved cannulated bone anchors that facilitate placement of the anchor in the bone.